1. Field of the Invention
The present invention relates to steering systems for automotive vehicles, and more particularly to a rack-and-pinion type steering apparatus having a pressure equalization system.
2. Description of the Prior Art
Rack-and-pinion type steering systems of automotive vehicles are well known in the prior art. Typically, rack-and-pinion type steering apparatus comprises a cylindrical steering gear housing attached to a body structure of the vehicle, and a steering rack shaft mounted within the housing for sliding movement therethrough. Opposite ends of the steering rack are coupled to left and right tie rods through ball joint assemblies to steer a set of road steering wheels in accordance with lateral displacement of the rack shaft. The rack-and-pinion type steering apparatus further includes a pair of protective boots of elastomeric material, each coupled at their one ends with the opposite ends of the tubular housing and at their other ends with the tie rods to encompass each joint assembly of the tie rods with the rack member, thus defining left and right ball joint chambers for sealing a steering gear and components of the ball joint assemblies against debris and foreign fluids.
However, the complete tight sealing provided by these protective boots brings an undesirable problem when the rack shaft is actuated to move the steering wheels of the vehicle to the right or to the left in accordance with the displacement of the rack shaft. Because each of the protective boots is fixed to the housing at one end and coupled with the movable tie rod at the other end in a condition where a steering wheel is retained in a position corresponding to straight ahead travel, during the displacement of the rack shaft one of the protective boots stretches, creating a negative pressure in the associated ball joint chamber, while the other protective boot compresses, creating a positive pressure in the associated ball joint chamber, thus causing a pressure differential between the left and right ball joint chambers that increases steering wheels to turning, quickly causes deterioration of the protective boots and even impairs the satisfactory operation of the steering apparatus.
Prior art teaches a number of means to eliminate this problem. One of such means consists of a valve means provided in these protective boots that communicates the interior of the protective boot with its exterior, allowing the relief of the pressure, or admitting air in the ball joint chamber during the compression thereof. This structure, however, did not prove itself efficient as it allows the entry of impurities with the air and, further, it is not cost effective, not durable and additionally causes damage to the protective boots in the places where these valves are attached.
The present invention provides an improved rack-and-pinion type steering apparatus for an automotive vehicle. The steering apparatus in accordance with the present invention comprises a cylindrical steering gear housing attached to a body structure of the vehicle, and a steering rack shaft mounted within the housing for sliding movement therethrough. Opposite ends of the steering rack shaft are coupled to left and right tie rods through ball joint assemblies to steer a set of road steering wheels in accordance with lateral displacement of the rack shaft. The rack-and-pinion type steering apparatus further includes a pair of protective boots of elastomeric material, each coupled at their one ends with the opposite ends of the tubular housing and at their other ends with the tie rods to encompass each joint assembly of the tie rods with the rack shaft, thus defining left and right ball joint chambers for sealing a steering gear and components of the ball joint assemblies against debris and foreign fluids. Furthermore, the steering apparatus of the present invention includes a pressure equalization system between the left and right ball joint chambers, so as to maintain substantially equal pressure therewithin. The pressure equalization system of the steering apparatus in accordance with the present invention includes an air path fluidly interconnecting the left ball joint chamber with the right ball joint chamber. The air path includes a longitudinal passage formed in the steering rack shaft, which through the communication passages in ball joint casings secured at the opposite ends of the steering rack shaft, is fluidly interconnects the left and right ball joint chambers.
Therefore, the improved rack-and-pinion type steering apparatus for the automotive vehicle of the present invention substantially improves operation of the steering apparatus and durability of the protective boots over the prior art in a way efficient and inexpensive in manufacturing.